Urinary excretion substances in patients with cystic fibrosis: risk of urolithiasis?

Abstract.

Patients with cystic fibrosis (CF) have an increased risk of urolithiasis/nephrocalcinosis. To determine potential mechanisms responsible, we studied the urinary excretion of lithogenic and stone-inhibitory substances and calculated the urinary saturation for calcium-oxalate (CaOx), brushite (CaHPO₄), and uric acid (UA). We examined 24-h urines in 63 patients with CF (34 female, 29 male) aged 5 months to 36 years. Renal ultrasonography was performed at the time of urine collection. Hyperoxaluria was found in 25 patients (range 0.51 – 1.71 mmol/1.73 m² per 24 h). Urinary Ca was increased in 13 patients (4.1 – 8.22 mg/kg per 24 h). Hyperuricosuria was found in 16 patients (5.2 – 18.0 mmol/1.73 m² per 24 h) and hypocitraturia in 14 patients (0.07 – 1.14 mmol/1.73 m² per 24 h). CaOx saturation was elevated in 26 patients, related to hyperoxaluria in 19 patients. CaHPO₄ saturation was increased in 19 patients and UA saturation in 11 patients. Urolithiasis in situ was diagnosed in 1 patient; 3 patients previously had renal stones; 4 patients had present nephrocalcinosis. Elevated excretion of lithogenic substances and urinary supersaturation might lead to the higher risk of urolithiasis/nephrocalcinosis in patients with CF.